What is Stars: Definition and 890 Discussions

A star is an astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but due to their immense distance from Earth they appear as fixed points of light in the sky. The most prominent stars are grouped into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated 1022 to 1024 stars, but most are invisible to the naked eye from Earth, including all individual stars outside our galaxy, the Milky Way.
A star's life begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. The total mass of a star is the main factor that determines its evolution and eventual fate. For most of its active life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and then radiates into outer space. At the end of a star's lifetime, its core becomes a stellar remnant: a white dwarf, a neutron star, or, if it is sufficiently massive, a black hole.
Almost all naturally occurring elements heavier than lithium are created by stellar nucleosynthesis in stars or their remnants. Chemically enriched material is returned to the interstellar medium by stellar mass loss or supernova explosions and then recycled into new stars. Astronomers can determine stellar properties including mass, age, metallicity (chemical composition), variability, distance, and motion through space by carrying out observations of a star's apparent brightness, spectrum, and changes in its position on the sky over time.
Stars can form orbital systems with other astronomical objects, as in the case of planetary systems and star systems with two or more stars. When two such stars have a relatively close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, such as a star cluster or a galaxy.

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  1. J

    Number of stars within 150 light years of us?

    I would like to know how many stars are within 150 light years of Earth. There must be a website somewhere that has the number, or perhaps a graph correlating distance with number of stars. I've done some searching, but you folks are much smarter than I am. Thanks
  2. B

    Do stars actually collide in galactic collisions?

    Will some of the stars of the Milky Way crash into those of Andromeda if these galaxies merge? What are the odds? How large a share of the stars will this happen to? Thanks
  3. J

    Why are galaxies shaped like spirals?

    why galaxies are having uneven distribution of stars, in the form of arms? actually stars should have been like a thin disk like distribution of stars.
  4. T

    Why aren't stars in a star cluster attracted to each other?

    If a globular cluster is a dense(relatively speaking) collection of stars, why don't the stars attract each other gravitationally? Why don't they all collide to form a mega-star?
  5. N

    Realism, or reaching for the stars

    The Goldwater scholarship application is approaching, and I think it's an excellent opportunity. However, I have a GPA less than the average of 3.95 (but above 3.8), have published no papers (but have been researching since late July), and all around am not a highly motivated individual. I'm...
  6. J

    Neutron Stars vs Black Holes: What's the Difference?

    what is the difference between a neutron star and a black hole?
  7. P

    Help me to get the names of all stars with their declination?

    I want to check circumpolar stars for the observer whose latitude is 26 degree 28 minute 12 second North (My office). From here, latitude = 26 degree 28 minute 12 second North, all stars with a declination higher than +63 degree 31 minute 48 second are such circumpolar stars. And stars with a...
  8. B

    How do massive stars like VY Canis not turn into black holes

    Apparently VY Canis Majoris is 30–40 solar masses, also there's R136a1 which is 265 solar masses. How do they remain stars with all that mass?
  9. mrspeedybob

    How do neutron stars emit light?

    It is my understanding that when an electron drops to a lower orbital that 2 photons of light are produced. The moving electric charge produces EM radiation just like moving charges in a radio transmitters antenna produce EM radiation. Energy in the form of radiation, heat, or whatever else, can...
  10. Z

    Collapsing Stars on the H-R diagram

    Hi, I've been looking at the Hertzsprung-Russel diagram and was wondering exactly what types of stars collapse to form a black hole? What temperature range/radius etc. turn into black holes. I understand that its most likely the supergiants that form black holes, but what about the giants? Are...
  11. D

    How many stars does one create and how many times can stars be

    How many stars does one create and how many times can stars be recycled into more stars?
  12. J

    Determining Mass Ratio of Double Star Systems with Spectroscopy

    Hi everybody When you have observed the complete revolution of a star around an other one, you can derive the mass of the double star system (the sum of the masses) by using the Kepler's third law. That's OK. I have heard that you can find the mass ratio of the system by using...
  13. Philosophaie

    Comparing Angular Rates of Star Rotation at Different Latitudes and Longitudes

    The Earth's rotational velocity at the Equator is 1,674.4 km/h or 465.1 m/s. The stars at the equator rotate at that same rate taking in account Precession at that particular time of the year and the longitude & latitude they are viewed from. Do the stars at the poles rotate faster then at the...
  14. R

    Lower mass limit for neutron stars?

    I was wondering, does anyone know of a lower limit on the mass of a neutron star from fundamental physics? That is, the smallest it could be before its pressure would make it explode. I don't mean the Chandrasekhar limit, as that's the upper limit for a white dwarf. Neutron stars occurring...
  15. B

    Best location for stars with naked eye

    These places seem great. Do places like these actually appear this way with the naked eye?
  16. O

    Geometry with polygons formed within drawn stars

    Homework Statement I'm working with the polygons on the interior of stars that have been drawn in a specific manner. For an example, I'm currently using a 16-gram. To construct the same one I have, you array sixteen vertices equidistant from one another around a central point (as in the...
  17. D

    Stars with 6 legs in seawater aquarium

    Recently I visited a sea water aquarium with tropical fish anemona, corals. At the glas walls I observed little (about 1 cm diameter) white stars with 6 legs. Now starfish have 5 legs, as far as I know. Any idea what this could have been?
  18. B

    How common is it for stars to have rocky bodies orbiting them?

    Hi all, I've read somewhere that at least 20% of our galaxy's stars have planets orbiting them? But what is the share if we include all kinds of rocky bodies? How likely is it that stars suck in everything without leaving any leftover material what so ever? I'm curious because the Drake...
  19. A

    Gravitational Potential Energy: Two Neutron Stars

    Homework Statement Deep in space, two neutron stars are separated (center-to-center) by a distance of 18 X 106 km apart. Neutron star A has a mass of 153 X 1028 kg and radius 52000 m while the neutron star B has a mass of 159 X 1028 kg and radius 72000 m. They are initially at rest with...
  20. C

    Are there undiscovered sister stars in our solar system?

    Hipparcus indicates that our supposed closest star alpha centuari is 742 marcs parallax, which corresponds to about 1.3 pc or 4.3 yrs away. Since stars form in multiple; hence our sun has sister stars at much closer distance, with higher parallax values. Also infrared telescope could be used to...
  21. M

    Why Do Some Stars Grow So Massive?

    Why are some stars so much more massive than others? Eta Carinae and The Pistol Star are 100X more massive than the Sun. When stars are forming, doesn't hydrogen fusion begin at about the same mass and density for all stars? Or does chemical composition and rotational velocity of the nebular gas...
  22. H

    Information about stars indeterminate?

    We break down the received light stectrum from a star into the individual wavelength components. From it we claim to know its composition, heat, distance and speed. Aren't there way more unknowns that knowns? For example, consider any arbitrary observed star with a certain color distribution...
  23. D

    Do Stars Flicker Colour & Intensity in the Night Sky?

    Hi, Do stars flicker colour and intensity in the night sky? I was in an argument with a friend of mine, and he told me stars can flicker 300nm in wavelength at 15Hz. I told him that I thought his eyes were just confusing change in intensity with colour. Was I wrong? Thanks:smile:
  24. S

    Temperature and Pressure at Center of Stars

  25. JaredJames

    One Million MPH Spinning Stars

    Don't know if anyone seen it, it's out today in a journal: http://www.msnbc.msn.com/id/42787604/ns/technology_and_science-space/ Sounds interesting, one of the first to catch my attention for a while (perhaps I just like big numbers...).
  26. T

    Core Collapse of Massive Stars

    Hello everydody. Well i need to write a repor (5 pages maximum) about Core Collapse of Massive Stars to my discipline Stellar Structure and Evolution . The problem is that i have read some books like https://www.amazon.com/dp/0387580131/?tag=pfamazon01-20 and i have no ideias. I gained...
  27. I

    Physics of laser pointer attachments: stars, butterflies, etc.

    http://nerdapproved.com/misc-gadgets/dolphin-laser-pointer-keychain/" So in the above image they have little attachments for laser pointers that can make different designs. I've played around with similar types of attachments for laser pointers and have never thought about the physics...
  28. P

    Dark matter really due to stars having some charge?

    Dark matter really due to stars having some charge?? I have an acquaintance who has a physics doctorate who argued the (to me) novel idea that dark matter doesn't really exist; that a plausible explanation of the observations suggesting it is that stars are sufficiently not exactly electrically...
  29. T

    Are Stars Limited to Galaxies or Can They Exist in Intergalactic Space?

    Do all stars have to be present inside of a galaxy? Or are there some stars that can be out side in intergalactic space? I was just curious. Thanks
  30. T

    Required mass for hydrogen burning in stars

    Hello all! I have to calculate the required mass to ignite the PP chain when the given temperature is 4*10^6K and \mu=0.62. (I know the answer is about 8% from the sun's mass)… I don't know exactly how to do it :-/ I know that (R/Rsun)=(M/Msun)^(3/7), The energy per nucleon in PP process is...
  31. N

    Why do stars twinkle and what causes it?

    Why do stars "twinkle?" I can't think of a better word for it Why are there 4 "spikes" coming out of the star? What optical phenomenon causes this? Why do some stars twinkle and others not? Thanks
  32. daisey

    Gravity and the Formation of Stars

    Earlier today I took a break from following the thread here on the Fukushima Nuc Plant problems (very interesting, by the way) and watched some TV, specifically a show I recorded on the formation of Stars. It reminded me of something that has been bothering me for some time - Gravity and how it...
  33. J

    The physics between stars and planets homework question?

    Homework Statement A binary star system consists of two equal mass stars that revolve in circular orbits about their center of mass. The period of the motion, T = 25.5 days, and the orbital speed v = 220 km/s of the stars can be measured from telescopic observations. What is the mass of...
  34. M

    Calculate Mass of Eri B & C: Solar Mass Ratio

    Homework Statement we are looking at two stars in the eridani system, eri B and eri C. the period of the system is 247.9 years. the system's measured trigonometric parallax is 0.201 arcseconds and the tru angular extent to the semimajor axis of the reduced mass is 6.89". the ratio of...
  35. C

    Astronomy, fraction of stars to have ever lived

    Homework Statement The question asks for the fraction of all 2M(sun) stars ever made in the Galaxy that are still burning on the main sequence. It assumes star formation at constant rate. The age of the Galaxy is 10GYRS To do this I imagine you use the salpeter IMF and find the constant...
  36. D

    Is the fate of black dwarfs to become neutron stars without proton decay?

    Will black dwarfs eventually quantum tunnel into neutron stars if proton decay doesn't occur?
  37. FtlIsAwesome

    What is the color of a neutron star?

    I'm wondering about the visual appearance of neutron stars up close. Do they continue to emit light like a white dwarf? Can cooled ones be gray or black? The xray emissions from pulsars will not be visible to us. Due to their high mass, they will bend light in a similar manner to a black hole...
  38. Ken G

    What is the truth about radiation pressure in stars?

    There is a great deal of misconception and misinformation surrounding the topic of radiation pressure in stars. I have found there to be a widespread idea that the cores of stars are held up primarily by radiation pressure, yet this is very rarely true. To see how bad the misinformation there...
  39. S

    What Causes the Lines in the Spectrum of a Star?

    I have 3 questions: 1)Does the lines in the spectrum of a star indicate the elements in its surface or also the inner parts? 2)when an electron goes to a higher state, it emits a photon with a wavelenght according to that transition, and we can see that line in the spectrum of that star? But...
  40. bcrowell

    Exploring Superfluidity in Neutron Stars: A Crayon Explanation

    I thought others might be interested in this: http://arxiv.org/abs/1011.6142 As a nuclear physicist, I don't find it surprising to hear that neutron stars are superfluid. Nuclei are superfluid. I'm not clear on the relationship between superfluidity and cooling. Can anyone explain this using...
  41. S

    Are Orbits of Close Binary Stars Truly Circular?

    in analysis of close binary stars, it is assumed that their orbits is circular and then by a rotating coordinate system, potential is obtained and then lagrangian points and so on... Is the orbit of CLOSE binary stars nearly circular in reality or is it assumed circular because otherwise it is...
  42. Q

    Why would two close stars have similar metallicity, but different color?

    This is the exact question: Stars in a globular cluster are observed to be one magnitude redder (in terms of B-V color, so the color excess E_(B-V) = 1, and extinction in the V band is 3.1) than other nearby stars having similar metallicity. What causes this? I'm aware of why two stars...
  43. J

    Astronomy, Luminosity of 100 solar mass stars

    This is just a small part of one of my problems. I need to find the luminosity of a stellar population containing 100 solar mass stars and one 20 solar mass star. I think that the 20 solar mass star will dominate, but I am not sure. Here is the formula to use: L/Lsun = (M/Msun)^3.5 I...
  44. S

    The eccentricity of binary stars' orbits

    Hi As two stars orbit their mutual center of mass in elliptical orbits, why are their eccentricity the same? And why is it the same as the one of reduced mass around center of mass? Thanks
  45. D

    Why is there still mostly hydrogen in pop I and II stars?

    I've heard in the past something along the lines of "every atom in your body came from an exploding supernova". Yet, I can't see how that could be true when there is still such an abundance of hydrogen. Wouldn't any hydrogen in a star prevent it from reaching supernova stage? Assuming...
  46. P

    Binary Stars energy loss calculation

    I can't seem to get any of the answers for this - please help! Two stars of equal mass M orbit a common centre. The radius of the orbit of each star is R. Assume that each of the stars has a mass equal to 1.5 solar masses (solar mass=2x10^30kg) and that the initial separation of the stars is...
  47. A

    Why Does Camera Flash Brighten Stars in the Sky?

    When I point a camera at the sky and use the flash, it brightens up all the stars I'm looking at (not just the ones on the screen). Does anybody know why this is?
  48. nukeman

    How do astronomers count stars in the Milky way? (procedure, method)

    Hey guys, What method[s] do astronomers use to count the stars in the galaxy to come up with a number ?
  49. H

    Do all stars belong to galaxies?

    This is probably quite a basic question but my mind has been ignited by the recent stargazing programs on the bbc so... Does every star have to be associated with a galaxy? For example, when looking through a telescope you see either individual stars or spiral galaxies - when looking at these...
  50. L

    Formation of neutron stars and black holes.

    First of all, I know that that very large stars tend to form black holes, and smaller stars, but still massive in comparison to our sun, tend to form neutron stars. My question is, if matter is lost when a star collapses into a black hole, but can still form one, why is it that it is a star...
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